1. Field of the Invention
The present invention relates to a magnetic head actuator, and more particularly to an electro-mechanical actuator for displacing a magnetic head on a rotary magnetic head drum assembly in a magnetic recording and reproducing apparatus such as a video tape recorder (VTR).
2. Description of the Prior Art
Some magnetic recording and reproducing apparatus, typically video tape recorders (VTR), employ a rotary magnetic head for recording and reproducing information signals on and from a magnetic tape. It is well known in the art that the image quality and functions of the existing VTRs have been greatly improved as a result of the great progress which the VTR technology has made so far. Efforts are now being made to develop a digital VTR for recording a digital video signal on a magnetic tape.
VTRs are generally used to record continuous images such as images of television broadcast programs and images represented by video signals that are produced by television cameras. Since magnetic tapes for use in VTRs have a large storage capacity, there is also an attempt to use a VTR as a mass storage device in a digital information processing system, for example.
According to other attempts, a VTR is used as an external auxiliary storage device for a computer, or as a device for successively recording computer graphics images after they have been processed and successively reproducing the recorded images as a moving image. In such applications, inasmuch as an information signal is to be recorded on a magnetic tape along one to several tracks, the VTR is required to record the information signal on the magnetic tape highly stably and reliably.
Various known processes are carried out in VTRs to record an information signal on a magnetic tape along a particular track or rewrite, i.e., record an information signal over, an existing information signal already recorded on a magnetic tape along a particular track. According to one process, a magnetic tape is rewound by pre-rolling until a rotary magnetic head is positioned ahead of a start-of-record position on the magnetic tape. Then, when an information signal is to be recorded, the magnetic tape is fed rapidly in the forward direction to move the start-of-record position on the magnetic tape past the rotary magnetic head at a certain speed, during which time the rotary magnetic head records the information signal along a certain number of tracks following the start-of-record position. According to another method, the angular position of a capstan motor is controlled by control pulses supplied thereto to stop a magnetic tape so that a rotary magnetic head faces a desired recording position on the magnetic tape, and then the rotary magnetic head records an information signal on the magnetic tape thus held at rest.
The former practice is relied upon in an assembly or insert recording mode in the editing function of the VTR. Since the magnetic tape is required to be repeatedly rewound and fed in the forward direction each time an information signal is to be recorded on the magnetic tape, a burden is imposed on the tape transport system and the magnetic tape itself, this practice is not suitable for frequent recording of information signals. The position of a track where an information signal is to be recorded is determined by the relative movement of the running magnetic tape and the rotary magnetic head. Consequently, it is difficult to position the track highly accurately with respect to the magnetic head. In addition, the intervals between recording cycles cannot be shortened because the prerolling of the magnetic tape is time-consuming.
The latter method is advantageous in that no tape rewinding is necessary, no large burden is imposed on the tape transport mechanism and the magnetic tape since an information signal is recorded while the magnetic tape is at rest, and the track where an information signal is to be recorded can be positioned highly accurately with respect to the magnetic head. However, tracks recorded on a magnetic tape by a rotary magnetic head while the magnetic tape is at rest are different in pattern from tracks recorded on a magnetic tape by a rotary magnetic head while the magnetic tape is running at a certain speed. Therefore, when the magnetic tape with information signals recorded thereon according to this method is to be played back while the magnetic tape is running, the tracks cannot accurately be followed by the rotary magnetic head. Furthermore, difficulty is experienced in recording, on the same magnetic tape, tracks while the magnetic tape is at rest, and tracks while the magnetic tape is running.
There have been developed different magnetic head actuators for controlling the position or path of rotary magnetic heads with respect to tracks on magnetic tapes. Known magnetic head actuators include an electrostrictive electro-mechanical magnetic head actuator as disclosed in Japanese patent publication No. 58-18686 and dynamic electro-mechanical magnetic head actuators as disclosed in Japanese laid-open patent publication Nos. 63-25821, 63-173217, and Japanese patent application No. 2-254934, for example.
The dynamic electro-mechanical magnetic head actuators are more advantageous than the electrostrictive electro-mechanical magnetic head actuators in that they can displace the magnetic head over a larger distance, do not require a high voltage for actuating the magnetic head, and can easily control the position or path of the magnetic head. However, the conventional dynamic electro-mechanical magnetic head actuators are also disadvantageous in that the magnetic head is actuated, it is displaced arcuately and cannot be maintained in good contact with the magnetic tape, and the magnetic head is subjected to leakage fluxes from the magnetic circuit of the magnetic head actuator, preventing information signals to be accurately recorded on and reproduced from the magnetic tape. The magnetic head actuators have leaf springs with magnetic heads supported thereon. Since the leaf springs tend to vibrate in many vibration modes, coil bobbins connected thereto also tend to move obliquely to the axis thereof. The magnetic heads, which are supported on the leaf springs in a cantilever fashion, are also liable to vibrate with the leaf springs, and hence to be tilted out of a desired azimuth with respect to the magnetic tape.